Hypochlorite and caustic oil treating process



OCI-HIQRITE AND CAUSTIC OIL TREATING PROCESS Ilacohus Wiihelmus Le Nobel and Adolf Christiaan Van Beast, Amsterdam, Netherlands, assignors to Shell Development Company, New York, N. Y., a corporation of Delaware No Drawing. Application September 7, 1954, Serial No. 454,638

Claims priority, application Netherlands September 11, 1953 3 Claims. (Cl. 196-29) The present invention relates to the treatment of hydrocarbon oils and particularly to the removal of mercaptans therefrom.

It is known to treat light hydrocarbon oils, particularly gasoline and kerosene, with an alkaline aqueous hypochlorite solution, such a sodium or calcium hypochlorite solution, in order to oxidize the mercaptans present in the hydrocarbon oil and also to remove, if desired, any sulfur compounds from the hydrocarbon oil.

Treatment of light hydrocarbon oils with a hypochlorite solution has often the disadvantage that during this treatment compounds are formed, especially sulfochlorides and sulfonyl chloride, which in the presence of water make the hydrocarbon oil corrosive towards metals, particularly iron. While such compounds can be removed by treating the hydrocarbon oil with an alkali metal hydroxide solution, this treatment proceeds too slowly for practical purposes. Many of the known anticorrosion agents, even those of a basic character, are not suitable for eliminating the corrosive properties of hypochlorite-treated hydrocarbon oils. This is especially the case when the hydrocarbon oil comes into contact with water, which frequently occurs in actual practice as during storage in tanks, during pumping or when the hydrocarbon oil is transported in another manner.

According to U. S. patent application Serial No. 425,727 the corrosive effect on metals of hypochloritetreated hydrocarbon oils can be suppressed by adding to the hydrocarbon oil a small quantity of certain monocarboxylic acids having from 12 to 30 carbon atoms. This process is simple but the quantities of the monocarboxylic acids which may be added in actual practice to the hypochlorite-treated hydrocarbon oil must in many cases, especially where gasoline is concerned, not be increased beyond a certain maximum since, if quantities of more than about 0.1% by weight of a monocarboxylic acid of this type are added to gasoline, the gum value of the gasoline becomes too high.

The principal object of the present invention is to provide an improved process for manufacturing sweetened hydrocarbon oils. A more particular object is to provide an improved method of hypochlorite-treating light hydrocarbon oils, especially gasoline. Another object is to provide an improved method of rendering a hypochlorite-treated hydrocarbon oil less corrosive to metals, especially iron and steel. Still another object is to provide a process for the removal of small quantities of organo-sulfur-chlorine compounds from hydrocarbon oils. Other objects will be obvious in the following description of the invention.

It has now been found that the corrosive compounds which are formed in a hydrocarbon distillate during the hypochlorite treatment thereof can be effectively removed by treating the hypochlorite-treated hydrocarbon oil with alkali metal mercaptides. Even at room temperature the mercaptides react with the corrosive corn- States Patent 2,766,182 Patented Oct. 9, 1956 pounds, such as sulfochlorides and sulfonyl chlorides, formed during the hypochlorite treatment, with the result that such compounds are converted to non-corrosive compounds, for example, disulfides.

From the U. S. patent specification No. 2,581,117 it has already been known to stabilize a hypochlorite-treated hydrocarbon oil against color deterioration and gum formation by adding to the oil an aqueous solution of an alkali metal sulfide. However, such a process has the disadvantage that free sulfur is formed by the reaction of the alkali metal sulfide with compounds such as sulfonyl chlorides which have been formed in the hydrocarbon oil during the hypochlorite treatment, so such a process is not a suitable method of preparing a noncorrosive product.

It is also known from the U. S. patent specification No. 2,022,942 to add free mercaptans to a hypochloritetreated hydrocarbon oil, particularly in the form of a mercaptan-containing hydrocarbon oil, one object being to decrease the corrosive effect of the oil on copper, but this measure is not adequate to eliminate the corrosive effect of a hypochlorite-treated hydrocarbon oil on iron or steel, and particularly not in the presence of Water. To this end it has been found necessary to add the corresponding alkali metal mercaptides instead of free mercaptans. Consequently, when in the process according to the invention a mercaptan-containing hydrocarbon oil is used, in addition to such hydrocarbon oil an alkali metal hydroxide solution is added at the same time to the hypochlorite-treated hydrocarbon, so that the mercaptans will react in the form of the corresponding mercaptides.

In the process according to the invention the upper limit of the quantity of added alkali metal mercaptides is determined by the requirement that the final oil product should give a negative doctor test, and as much should be added as is necessary to reduce the acid number of the oil product to 0.01 or less.

The process of the invention is restricted to treating the hypochlorite-treated oil with alkali mercaptides not containing a substantial proportion of alkali metal methyl mercaptides. This is because such methyl mercaptides will react with compounds formed in the hypochlorite treatment to produce dimethyl disulfide. As contrasted with the higher disulfide, this compound is evil-smelling and would degrade the resulting oil product containing it to such an extent that it would not be commercially acceptable.

The invention therefore encompasses a process for preparing a hypochlorite-treated light hydrocarbon oil having a reduced corrosive effect on iron, characterized in that the hydrocarbon oil, after the hypochlorite treatment, is treated with an alkali metal mercaptides or mixture thereof, each of which mercaptides having a hydrocarbon radical with at least 2 carbon atoms, in such a quantity that the acid number of the hydrocarbon oil is reduced to 0.01 or less, and the final product gives a negative doctor test.

The alkali metal mercaptides may be derived either from aliphatic or aromatic mercaptans (thiophenols).

As already mentioned the process of the invention can be carried out by treating the hypochlorite-treated hydrocarbon oil with a combination of an alkali metal hydroxide solution and a mercaptan-containing hydrocarbon oil. In such a case the mercaptan-containing oil must first be processed to insure the exclusion of methyl mercaptan and also hydrogen sulfide therefrom. Accordingly, the mercaptan-containing oil must first be freed of those components which have boiling points below 25 C. (that is, 25 C. in the unmixed state). This can be accomplished conveniently by any conventional separation technique, for example, distillation.

A particularly advantageous method according to the invention is a combined process of hypochlorite treatment and mercaptide after-treatment which comprises first eliminating from the sour hydrocarbon oil those components which have boiling points below 25 C., then splitting the sour oil into two streams, one of which is hypochloritetreated in the conventional manner and the other of which is added, together with an alkali metal hydroxide solution, back into the hypochlorite-treated stream. In this manner a mercaptan-free hydrocarbon oil is obtained which, even in the presence of water, has no corrosive effect or at least a considerably reduced corrosive effect on metals, particularly on iron. The mercaptans in the part of the hydrocarbon oil which has not been treated with hypochlorite react with the corrosive components of the hypochlorite-treated part, and thus both of these deleterious materials are rendered innocuous.

To promote the desired reaction, the hydrocarbon phase, which consists of the mixture of hypochloritetreated hydrocarbon oil and mercaptan-containing hydrocarbon oil, is thoroughly stirred with the added alkali metal hydroxide solution. This stirring is continued until the corrosive components of the hypochlorite-treated hydrocarbon oil, particularly the sulfonyl chlorides, which are the most difficult to convert, are rendered harmless by the reaction with the alkali metal mercaptides. A suitable stirring device is the turbomixer. The reaction is generally completed after 340 minutes. The reaction is suitably carried out at room temperature, though, if desired, higher or lower temperatures can be applied.

The quantities of the hypochlorite-treated hydrocarbon oil and the mercaptan-containing hydrocarbon oil, which are reacted in the simultaneous presence of an alkali metal hydroxide solution, may vary between certain limits. The lower limit for the quantity of the mercaptan-containing hydrocarbon oil is determined by the requirement that the acid number of the final product should not exceed 0.01. The upper limit is determined by the requirement that the final product should give a negative doctor test. It is, of course, obvious that these proportions will vary depending upon the particular oil being treated, but it is only necessary to use these two simple tests to determine the allowable limits quickly and easily.

The quantity and. the concentration of the alkali metal hydroxide solution which is added, in combination with the mercaptan-containing hydrocarbon oil, to the hypo chlorite-treated hydrocarbon oil may vary within wide limits. In general the desired reaction is promoted by using more concentrated solutions of alkali metal hydroxide. Aqueous as well as alcoholic alkali metal hydroxide solutions are useful. In actual practice aqueous solutions are generally preferred because they are cheaper. Aqueous solutions of potassium hydroxide, or preferably sodium hydroxide, at concentrations of 10-30% by weight are very suitable. Of such solutions a quantity is added of 5-50, more particularly of -20% by volume, calculated on the hydrocarbon phase, i. e., the mixture of hypochlorite-treated hydrocarbon oil and mercaptan-containing hydrocarbon oil.

Mercaptans as such or mercaptans dissolved in another solvent than the hypochlorite-treated hydrocarbon oil, but in either case in combination with an alkali metal hydroxide solution, can also be added to the hypochloritetreated hydrocarbon oil.

It is also possible to add to the hypochlorite-treated hydrocarbon oil a solution of alkali metal mercaptides (each of which mercaptides having a hydrocarbon radical of at least 2 carbon atoms) in an alkali metal hydroxide solution. This solution should be free or practically free from alkali metal sulfide and from methyl mercaptide. A suitable solution is, for instance, an aqueous alkali metal hydroxide solution which contains a mercaptan solutizer and has been used for extracting mercaptans from a hydrocarbon oil previously freed from components boiling below C.

Upon completion of the reaction of the corrosive components of the hypochlorite-treated hydrocarbon oil with alkali metal mercaptides, the alkali metal hydroxide solution employed is removed. The hydrocarbon oil thus obtained shows a negative doctor test and the content of corrosive components formed during the hypochlorite treatment is considerably reduced.

if, after the treatment described, the hydrocarbon oil still contains small amounts of corrosive components formed during the hypochlorite treatment, the corrosive effect thereof can be inhibited by adding to the hydrocarbon oil, in accordance with the disclosure of the U. S. patent application Serial No. 425,727, a small amount, particularly 0.0l0.l% by weight, of an aliphatic or cycloaliphatic monocarboxylic acid having from 12 to 30 carbon atoms and a solubility in water no greater than 0.1 gram per liter at 20 C., for example oleic acid.

It is also possible to add to the hydrocarbon oils obtained in the manner indicated other stabilizers, such as other anti-corrosion agents, for example dicarboxylic acids having at least 8 carbon atoms, anti-oxidants, for instance alkyl phenols or aromatic amines, and gum inhibitors. The hydrocarbon oils may also be provided with other additives, for instance anti-knock agents, such as tetra alkyl lead, iron carbonyl and dicyclopentadienyl iron, scavengers, such as ethylene dichloride, ethylene dibromide and tricresyl phosphate, and dyes.

After the treatment with alkali metal mercaptides to remove corrosive components, the hydrocarbon oil may, if desired, be subjected to an after-treatment with, for example, an aqueous alkali metal hydroxide solution and/ or water and/or an adsorbent.

The present invention is particularly suitable in the treatment of hydrocarbon oils having end-points of 350 C. and less, and especially kerosene and gasoline.

The process is not only suitable for straight-run hydrocarbon oils, but it is also applicable to hydrocarbon oils obtained by cracking or reforming.

The hypochlorite treatment can be carried out by any of the known methods. Most suitable is a treatment with an aqueous alkaline sodium or calcium hypochlorite solution. Suitable aqueous solutions are those containing 0.1%5% by weight, particularly 0.3 %1% by weight, of NaOCl and 1%30% by weight, particularly 2%10% by weight, of NaOH. These solutions may, moreover, contain NaCl, generally in a quantity varying from 1% to 25% by weight, particularly from 1% to 5% by weight.

The quantity of the hypochlorite solution with which the hydrocarbon oil is brought into contact can vary within Wide limits. In general the hypochlorite solution is used in an excess with respect to the quantity which is theoretically just sufiicient to oxidize the mercaptans present in the hydrocarbon oil to disulfides. This is due to the fact that in the hypochlorite treatment of the hydrocarbon oil, other compounds besides disulfide are produced which require more oxygen for their formation. Generally, satisfactory results are obtained if hypochlorite is used in an excess of 5 to 15 times, particularly 10 times, the theoretical quantity. A particular advantage of the present invention, in this respect, is that a greater flexibility of treating conditions is possible without imparting to the product an unsatisfactory corrosivity.

The treatment of the hydrocarbon oil with a hypochlorite solution is usually carried out at normal or slightly reduced or elevated temperatures. Suitable temperatures are those within the range of 0 C. to 50 C., more particularly with the range of 15 C.35 C.

The treatment of the hydrocarbon oil with the hypochlorite solution is etfected by mixing the two phases. Depending upon the composition of the hypochlorite solution, its quantity, the quantity of the mercaptans to be oxidized and the intensity of stirring, the hydrocarbon oil and the hypochlorite solution are kept in contact with each other during a period varying from 1 to 30 minutes.

The following examples are presented in order to The starting material was a straight-run Iraq gasoline which had a mercaptan sulfur content of 0.0224% by weight and an end boiling point of about 150 C. One part by volume of this was treated with 0.35 parts by volume of an aqueous solution containing 0.5% by weight of NaOCi and 4% by weight of NaOH for minutes at a temperature of 20 C. These proportions correspond to 10 times the theoretical quantity of hypochlorite solution required for oxidizing the mercaptans present in the gasoline to disulfides.

To this hypochlorite-treated gasoline, which had an acid number of 0.10 mg. KOH/ gram gasoline, 60% by volume of a straight-run Kuwait gasoline (containing no components boiling below 25 C.) having a mercaptan sulfur content of 0.0133% by weight, was added together with 10% by volume of a 10% by weight aqueous NaOH solution, after which the mixture was thoroughly stirred in a turbomixer for 6 minutes at a temperature of 20 C. Subsequently the aqueous NaOH solution was separated.

A gasoline product was obtained which had an acid number or" less than 0.001 mgKOH/gram gasoline and a mercaptan sulfur content of 0.0005% by weight. This gasoline gave a negative doctor test.

The corrosive effect of this gasoline product on iron in the presence of water was determined by the following test.

A glass fiasl: was filled with 1 liter of the gasoline and 10 cc. of distilled water. The gasoline and the water were shaken for 1 minute, and then allowed to settle. A pre-weighed iron strip was then suspended in the gasoline. The flask was then closed and maintained at a temperature of 38 C. for 10 days. At the end of this period the iron strip was washed with benzene to remove any rust that might have formed and which had not already scaled off. Whatever rust was still attached to the strip was removed electrolytically in a strong aqueous sodium hydroxide solution. The loss of weight of the iron strip and thus the measure of corrosion was determined by weighing.

This test was applied to a sample of the hypochloritetreated straight-run Iraq gasoline, before further treatment with the mercaptan-containing straight-run Kuwait gasoline and aqueous NaOH solution, and to a sample of the said Iraq gasoline after the mercaptide treatment. The results of these tests are shown in the following table:

Weight loss of iron strip Appearance of iron strip in mg. per at the end of the test 25 sq. em.

Hypochlorite-treated Iraq gas- 90 Completely rusted on eioliue before mercaptide ther side; rust on bottom treatment. of the flask.

Same aiter mercaptide treat- 26 Slight rust formation; no ment. rust on bottom of the From this table it appears that the after-treatment of the hypochlorite-treated gasoline with a mercaptan-containing gasoline and an aqueous sodium hydroxide solution results in a marked decrease in the corrosive effect of the gasoline on iron in the presence of water.

Example II components boiling below 25 C.) having a mercaptansulfur content of 0.0130% by weight was added together with 10% by volume of a 20% aqueous NaOH solution, after which the mixture was thoroughly stirred in a turbomixer for 6 minutes at a temperature of 20 C. Subsequently the aqueous NaOH solution was separated.

The gasoline product obtained had an acid number of 0.001 mg. KOH/gram gasoline and a mercaptan-sulfur content of nil.

Example III This example was carried out in the same manner as Example II, the only difierence being that 20% by volume instead of 10% by volume of the straight-run Kuwait gasoline was added to the hypochlorite-treated gasoline together with the aqueous NaOH. The acid number of the gasoline thus obtained was also 0.001 mg. KOH/ gram gasoline, but the mercaptan-sulfur content thereof was now 0.0003% by weight. This gasoline however, gave a negative doctor test.

Example IV The starting material here was a straight-run Kuwait gasoline which had a mercaptan-sulfur content of 0.0133% by weight and an end boiling point of 150 C. This was treated in the same manner as indicated in Example I with 10 times the theoretical quantity of an aqueous solution containing 0.5% by weight of NaOCl and 4% by weight of NaOH.

To this hypochlorite-treated gasoline, which had an acid number of 0.022 mg. KOH/gram gasoline, 15% by volume of a straight-run Iraq gasoline (containing no components boiling below 25 C.) having a mercaptansulfur content of 0.023% by weight was added together with 10% by volume of a 10% aqueous NaOH solution, after which the mixture was thoroughly stirred in a turbomixer for 6 minutes at a temperature of 20 C. Subsequently the aqueous NaOH solution was separated.

The gasoline product obtained had an acid number of 0.001 mg. KOH/gram gasoline and a mercaptan-sulfur content of 0.0004% by weight. The gasoline gave a negative doctor test.

Example V The starting material in this example was a sulfur-free and aromatic-free gasoline fraction having an A. S. T. M. distillation range of 70 C. to C. Tertiary Cs mercaptans were added in such a quantity that the gasoline had a mercaptan-sulfur content of 0.0156% by weight. This mercaptan-containing gasoline was then treated in the manner indicated in Example I with 10 times the theoretical quantity of an aqueous solution containing 0.5 by weight of NaOCl and 4% by weight of NaOH.

To the hypochlorite-treated gasoline, which had an acid number of 0.21 mg. KOH/gram gasoline and a mercaptan-sulfur content of nil, 0.0122% by weight of mercaptan sulfur in the form of tertiary Cs mercaptans was then added, together with 20% by volume of a 20% aqueous NaOH solution, after which the mixture was thoroughly stirred in a turbomixer for 6 minutes at a temperature of 20 C. Subsequently the aqueous NaOH solution was separated.

The gasoline product obtained had an acid number of 0.002 mg. KOH/gram gasoline and a mercaptan-sulfur content of nil.

Twenty percent by volume of a 20% aqueous NaOH solution was added to the above-described hypochloritetreated gasoline, which had an acid number of 0.21 mg. KOH/gram gasoline, this time without mercaptans being added. The gasoline, after having been thoroughly stirred in a turbomixer with the NaOH solution for 1 hour at a temperature of 20 C. was found to have an acid number of 0.06 mg. KOH/ gram gasoline, while after the mixture had been stirred for 2 hours, the acid number fell to 0.05 mg. KOH/ gram gasoline.

On addition of the above quantity (0.0122% by weight of mercaptan sulfur) of tertiary Cs mercaptans to the hypochlorite-treated gasoline, which had an acid number of 0.21 mg. KOH/gram gasoline, but now without the addition of an aqueous alkali metal hydroxide solution, it was found that the acid number of the gasoline had remained unchanged after thoroughly stirring the mixture in a turbomixer for 1 hour.

Example VI The starting material was a straight-run Kuwait gasoline which had a mercaptan-sulfur content of 0.0133% by weight and an end boiling point of 150 C. and which had been treated in the same manner as indicated in Example I with times the theoretical quantity of an aqueous solution containing 0.5% by weight NaOCl and 4% by weight of NaOH.

About 0.009% by weight of thiophenol together with 20% by volume of a 10% aqueous NaOH solution was added to this hypochlorite-treated gasoline, which had an acid number of 0.012 mg. KOH/ gram gasoline, after which the mixture was thoroughly stirred in a turbomixer for 3 minutes at a temperature of 20 C. Subsequently the aqueous NaOH solution was separated.

Thus a gasoline was obtained which had an acid number of 0.001 mg. KOH/ gram gasoline and a mercaptansulfur content of less than 0.0004% by weight. This gasoline gave a negative doctor test.

We claim as our invention:

1. A process for producing a doctor sweet gasoline having an acid number not over 0.01 mg. KOH/gram of gasoline from a sour gasoline feed which comprises: (1) eliminating from the sour gasoline those components which have boiling points below 25 C.; (2) splitting the resulting sour gasoline into major and minor streams,

the minor stream being from 10 to of the major stream; (3) treating the major stream with an aqueous alkaline hypochlorite solution from 5 to 15 times that theoretically required to convert mercaptans present in the major stream to disulfides; (4) separting the resulting treated gasoline stream containing dissolved chlorine compounds from the aqueous solution; (5) mixing this treated major stream and the minor sour gasoline stream and intimately contacting the mixture with an aqueous alkali metal hydroxide solution to produce a doctor sweet gasoline having an acid number not over 0.01 mg. KOH/gram of gasoline; and (6) separating the doctor sweet gasoline from the aqueous solution.

2. A process in accordance with claim 1, wherein the amount of hypochlorite utilized in step (3) is about 10 times that theoretically required.

3. A process in accordance with claim 1, wherein the aqueous alkaline hypochlorite solution utilized in step (3) contains 0.31% by weight NaOCl and 2-10% by weight of NaOH, and wherein the aqueous alkali metal hydroxide solution utilized in step (5) is aqueous sodium hydroxide having a concentration of 10-30% by weight of sodium hydroxide.

References Cited in the file of this patent UNITED STATES PATENTS 1,927,068 McClauhry et a1 Sept. 19, 1933 2,022,942 Schulze et al. Dec. 3, 1935 2,581,117 Love Jan. 1, 1952 2,626,232 Love Jan. 20, 1953 2,702,237 Sorg Feb. 15, 1955 2,717,856 Ricards et al Sept. 13, 1955 2,721,166 Earhart Oct. 15, 1955 

1. A PROCESS FOR PRODUCING A DOCTOR SWEET GASOLINE HAVING AN ACID NUMBER NOT OVER 0.01 MG. KOH/GRAM OF GASOLINE FROM A SOUR GASOLINE FEED WHICH COMPRISES: (1) ELIMINATING FROM THE SOUR GASOLINE THOSE COMPONENTS WHICH HAVE BOILING POINTS BELOW 25% C., (2) SPLITTING THE RESULTING SOUR GASOLINE INTO MAJOR AND MINOR STREAMS, THE MINOR STREAM BEING FROM 10 TO 60% OF THE MAJOR STEAM; (3) TREATING THE MAJOR STREAM WITH AN AQUEOUS ALKALINE HYPOCHLORITE SOLUTION FROM 5 TO 15 TIMES THAT THEORETICALLY REQUIRED TO CONVERT MERCAPTANS PRESENT IN THE MAJOR STREAM TO DISULFIDES; (4) SEPARATING THE RESULTING TREATED GASOLINE STREAM CONTAINING DISSOLVED CHLORINE COMPOUNDS FROM THE AQUEOUS SOLUTIONS; (5) MIXING THIS TREATED MAJOR STREAM AND THE MINOR SOUR GASOLINE STREAM AND INTIMATELY CONTACTING THE MIXTUERE WITH AN AQUEOUS ALKALI METAL HYDROXIDE SOLUTION TO PRODUCE A DOCTOR SWEET GASOLINE HAVING AN ACID NUMBER NOT OVER 0.01 MG. KOH/GRAM OF GASOLINE; AND (6) SEPARATING THE DOCTOR SWEET GASOLINE FROM THE AQUEOUS SOLUTION. 